The invention relates to screw compressors and, more particularly, to screw compressors used in water cooled chillers and the like and balancing of axial thrust in same.
Screw compressors used in water cooled chillers are typically of the oil flooded type. Axial thrust in this type of device is considerably high, typically resulting in the need for multiple bearings to carry the load.
If this thrust is not balanced or otherwise reduced, bearings and other compressor components can rapidly wear, causing the need for frequent repair.
Balancing pistons have been devised for balancing this thrust, but are positioned at the discharge end of the screw and tend to block the discharge porting of the male rotor of the compressor. Blockage of the discharge or exit port can be in the range of approximately 15% with such devices, and can result in substantial pressure losses. In addition, liquid trapping can result.
It is clear that the need remains for an apparatus for satisfactorily balancing axial thrust of screw compressors for water cooled chillers and the like.
It is therefore the primary object of the present invention to provide a screw compressor having an axial thrust balancing device.
It is a further object of the present invention to provide such a screw compressor which further includes a motor cooling apparatus.
Other objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages have been readily attained.
In accordance with the present invention, a screw compressor having balanced axial thrust is provided which comprises a housing having a fluid inlet and a fluid outlet; a rotor disposed in said housing for receiving low pressure fluid from said inlet and discharging increased pressure fluid from said outlet, said rotor having a discharge end and a motor end; a balance piston arranged to exert a balancing force on said motor end of said rotor; and a conduit for conveying a high pressure fluid to said balance piston so as to exert said balancing force.
In accordance with preferred aspects of the present invention, the balance piston can be provided as a portion of the motor rotor end ring.
In accordance with a further preferred aspect of the present invention, an end cover for the screw compressor is provided which is adapted for conveying high pressure fluid to the balance piston, and may also be adapted for conveying cooling fluid to the motor.